1. Field of the Invention
The present invention relates to a method of punching blanking core pieces of a rotor core of a magnet-embedded motor, and a stacked core obtained by stacking the core pieces.
2. Description of the Related Art
In designing a magnet-embedded motor, there is a tendency of decreasing the width of a bridge formed between a magnet insertion hole and an outer circumference of a rotor core so as to improve the characteristics of the motor (refer to JP-A-2013-66339).
FIG. 8A illustrates a part of a rotor core 70 according to an example in the related art. In this example, the width of each of bridges 74 and 75 between a pair of magnet insertion holes 71 and 72 and an outer circumference 73 is further reduced. As illustrated in FIGS. 8B and 8C, the rotor core 70 is manufactured by forming core pieces 77 via a plurality of processes. FIG. 8A also illustrates permanent magnets 71a and 72a. 
In the manufacturing of the core piece 77, as illustrated in FIG. 8B, a stripper 79 holds a magnetic steel sheet 78 on a die 80, and the magnet insertion hole 71 (72) is formed by punching with a die 81. Subsequently, as illustrated in FIG. 8C, a stripper 82 holds the magnetic steel sheet 78 on a die 83 at a downstream station, and the core pieces 77 are punched out from the magnetic steel sheet 78 using a punch 84 and fall into the die 83 to be stacked on each other. FIGS. 8B and 8C indicate a bridge 85 (equivalent to the bridges 74 and 75 in FIG. 8A).